This invention relates to a power supply for electrical equipment requiring direct current, the power supply being operable to convert an alternating current line voltage to direct current with an improved input power factor.
Conventional AC to DC converters are well known, which include a full-wave bridge rectifier and a storage capacitor. As is also well known, such a converter causes the line current to become non-sinusoidal, producing an input power factor between 0.6 and 0.7. Due to this relatively poor power factor, the circuit draws substantially more current than would be true if the load were resistive (a power factor of 1.0). A power supply with an input power factor of 0.6 to 0.7 is disadvantageous because it delivers substantially less power at a particular input current than does a power supply with a power factor of close to 1.0.
The foregoing is well known to those skilled in this art, and power supply circuits including power factor correction components have been provided. For example, the following listed U.S. Pat. Nos. relate to such arrangements:
______________________________________ Number Date ______________________________________ 4,074,344 02/14/78 4,677,366 06/30/87 4,777,409 10/11/88 4,801,887 01/31/89 4,816,982 03/28/89 4,831,508 05/16/89 4,940,929 07/10/90 5,003,454 03/26/91 5,181,159 01/19/93 5,301,095 04/05/94 ______________________________________
While the circuits described in the above patents may perform satisfactorily, there is a continuing need for a power supply including an improved power factor correction circuit, which is less complicated and less expensive than those of the prior art.
It is therefore a general object of the present invention to provide an improved power supply including a power factor correction circuit.